Electronic devices may operate using one or more supply voltages applied to the device. In addition to applied supply voltages, electronic devices may generate additional voltages, such as by boosting or otherwise altering applied supply voltages.
Memory devices may generate a voltage that may have a value between a supply voltage and ground. The generated voltage may be used for any of a variety of purposes, including, but not limited to, being applied to one side of a capacitor used in a memory cell or being applied to a digit line used to address memory cells.
Voltages generated by electronic devices may be generated in a manner designed to reduce the variability of the generated voltage. FIG. 1 is a schematic illustration of a conventional voltage generator configured to generate a voltage VC2. The voltage generator 100 includes a pull down amplifier 105 and a pull up amplifier 110. The pull down amplifier 105 receives the generated voltage VC2 at a first input and a high threshold voltage (‘High’) at a second input. The pull down amplifier 105 has an output coupled to the gate of a transistor 115. The pull up amplifier 110 receives the generated voltage VC2 at a first input and a low threshold voltage (‘Low’) at a second input. The pull up amplifier 110 has an output coupled to the gate of a transistor 120. The transistor 120 is a p-FET transistor coupled between a supply voltage VCCX and the generated voltage VC2. The transistor 115 is an n-FET transistor coupled between the generated voltage VC2 and a ground reference voltage. The generated voltage VC2 is accordingly generated at the drains of the transistors 120 and 115.
The voltage generator 100 accordingly ensures that the generated voltage VC2 is maintained between the High and Low threshold voltages. If the voltage VC2 falls below the low threshold voltage Low, the pull up amplifier 110 is configured to turn on the transistor 120 to pull VC2 up to the low threshold voltage. If the voltage VC2 rises above the high threshold voltage High, the pull down amplifier 105 is configured to turn on the transistor 115 to pull VC2 down to the high threshold voltage. The voltage VC2 may, however, vary between the high and low threshold voltage values. The range between the high and low threshold voltage values may be referred to as ‘dead band.’
The high and low threshold voltage values may be generated in any of a variety of ways. FIG. 2 is a schematic illustration of a circuit for generating the high and low threshold voltages (‘High’ and ‘Low’) of FIG. 1. A resistor divider 200 includes resistor 205, variable resistor 210, and resistor 215. The resistors 205, 210, and 215 are coupled in series between supply voltages Vcc and ground. The values of High and Low may be determined by setting or varying the value of the variable resistor 210.